Device for scour protection of offshore structures

ABSTRACT

A device for scour protection of offshore structures includes one or more elastic plates made of rubber and connected to each other, and weight elements which are fastened on the plates by fasteners.

FIELD OF THE INVENTION

The invention relates to an apparatus for scour protection of offshoreconstructions.

BACKGROUND OF THE INVENTION

Scouring is understood to be erosion phenomena of a water-covered bottomcaused by currents in the region of the offshore constructions. Adisadvantage of known protective measures is that they are complicated,but nevertheless insufficient with regard to their protective effect. Inthe offshore sector, for example in the case of monopiles of wind energysystems, it is the state of the art to pile up approximately 300 to 1000metric tons of stones as scour protection. However, these stones produceharmful currents that prevent sedimentation of sand and in this wayactually accelerate scouring. In addition, there is the risk thatfalling stones or stones that sink away as the result of the currentmight damage the ocean cable connection of the offshore wind energysystem.

It is also known to use geotextile containers filled with sand, weighingabout 1000 kg, as scour protection. In this connection, however, itcannot be ensured that these will maintain their position on the oceanfloor once they have assumed it. They furthermore form an angle to theocean floor and can thereby actually promote scouring. Also, thesecontainers and stones can sink into the ocean floor as the result offlow events, and in this case must be introduced again, which causescontinuous costs. Here, too, damage to the ocean cable is possible.Furthermore, both stones and containers cannot be placed precisely, interms of location, starting from a certain water depth.

A third possibility that is frequently utilized consists in not usingany scour protection at all, accepting scouring that occurs, and hoping,in this connection, that the scouring that develops will not exceed acertain depth. However, the foundation of a monopile, for example, thenhas to be introduced deeper into the ocean floor by this depth, whichcauses additional construction costs. Furthermore, the laid ocean cablesof the offshore construction can be exposed by the scouring and/or itsconnections can be damaged or destroyed as the result of currenteffects.

Not only stones but also containers can form a permanent hazard locationfor fishing after the systems are decommissioned, since theseapparatuses are generally not removed, because of the very high costs.

BRIEF SUMMARY OF THE INVENTION

The present invention was developed against the background of the stateof the art described above. It is therefore the task of the invention topropose an apparatus for scour protection of offshore constructions,which offers durable, cost-advantageous, and, in this connection,effective protection.

This task is accomplished in that the apparatus comprises one or moreelastic panels composed of rubber and weight elements that are fastenedonto the panels by means of suitable fastening means. Fastening isunderstood to be permanent and secure fixation of the weight elements onthe panel or panels, specifically even if the elastic panel or theelastic panels are pulled or pressed down by the weight elements, inorder to thereby form an advantageous hydrodynamic shape. Suitablefastening means are, for example, screws with nuts. An advantageoushydrodynamic shape is understood to mean that the panel or the panelsis/are curved downward in the edge region of the apparatus, whereby theback or underside of the panels serves as a contact surface for thesubsurface, and the front or top of the panels serves as a run-upsurface and as protection against eroding sand eddies and water eddies.The panels composed of rubber can be laid directly onto the sand surfaceor seabed surface in the region of the offshore constructions, below thewater or ocean surface, or can also lie completely or partly under theseabed surface. In this connection, they have the advantage that theycan adapt to the course of the seabed surface and can absorb the energyof the waves or eddies by means of their elastic properties.Furthermore, they are resistant to salt water and no corrosion occurs.Because of the strength and durability of the rubber, the apparatus istherefore maintenance-free. The rubber can be produced from naturalrubber, in environmentally friendly manner. A further advantage is thatthe apparatus is not hazardous in the event of a collision withwatercraft. The elastic panel or the elastic panels composed of rubberare fixed in place at the locations to be protected, using the securelyand permanently affixed weight elements.

Advantageous embodiments of the invention, with additionalcharacteristics, are described below.

It has proven to be optimal if the elastic panel or the elastic panelscomposed of rubber have a thickness of one to two centimeters. Theweight elements are preferably fastened onto the top of the elasticpanels in the edge region of the apparatus. The surface formed by thepanels is curved by means of the force exerted on the panels by theweight elements and by means of the recovery force brought about bytheir elasticity, and a particularly advantageous, hydrodynamic shape isformed, which serves as a run-up surface for water waves or pressurewaves. The force of the pressure waves is taken up, absorbed, andconducted away from the offshore constructions. If the ground underneaththe weight element subsides or is washed away, then the weight element,together with the panel, moves downward, thereby restoring theprotective effect. An ocean cable laid under the elastic panels composedof rubber is optimally protected and increases the operationalreliability of the system. The proposed apparatus for scour protectionfurther has the advantage, in the offshore sector, that it can beremoved with a single crane movement, and leaves a barrier-free oceanfloor behind.

In a preferred embodiment, the apparatus forms or the elastic panelforms or the elastic panels connected with one another form a diskhaving a circular or approximately circular contour, at the center pointof which the offshore construction is disposed. The weight elements arethen particularly fastened on along the edge region of the disk. Theelastic panel or the elastic panels connected with one another are thencurved most strongly downward along the edge region of the disk, wherebythe curvature decreases in the direction toward the centrally disposedoffshore construction and makes a transition into a flat surface.

It has proven to be advantageous if the radius of the apparatus is aboutthree times as long as the radius of the offshore construction in theplane in which the apparatus is disposed or fastened onto the offshoreconstruction.

The weight elements have an approximately rectangular base surface, thelongitudinal axis of which points in the direction of the offshoreconstruction, in each instance.

If the weight elements are made of metal, a large mass with great weightis achieved at a small volume.

The weight elements can have the shape, in longitudinal section and/orin transverse section, of an equilateral, symmetrical trapezoid, whichnarrows toward the top, whereby its corners are preferably rounded off.

The weight elements can have an indentation on the underside, which isdomed inward, in concave manner, in cross-section.

The weight elements serve not only for weighing down a panel or multiplepanels. Depending on their size and their arrangement, they havedifferent requirements and tasks to fulfill.

The weight elements are fastened onto the panel or the panels and havethe task of holding the apparatus on the ground at certain points. Themass of the weight elements, among other things, must be determined as afunction of the spacing and the water depth and the wave height to beexpected, as well as the flow velocity of the water. They must balanceout different pore pressures caused by wave action, i.e. the panel issupposed to rise and fall between the weight elements. However, the sandremains underneath and is held in place. In order for this to be madepossible, water-tight fastening onto the offshore construction to beprotected must take place, and weight elements positioned at the edgemust be provided on the outside, at the edge.

The edge weight elements must have a specific, flow-advantageous shape,and must be oriented in a specific manner and at a specific distancerelative to one another. The correct weight size and the least possibleflow resistance must be selected for the application case, in eachinstance. Metal weight elements having a small surface area and greatweight are advantageous. Also, the distance between the weight elements,relative to one another, is important. These weight elements must beselected, in terms of weight, shape, and surface, depending on theconditions of use, in such a manner that they work themselves into theocean floor at the edges, on their own, under the effect of currents andwaves, and thereby the panel is sealed off at the edge. In thisconnection, no fold or opening is allowed to form. At the same time,however, this edge must adapt to any unevenness of the ocean floor.Here, the particular configuration of an advantageous hydrodynamic shapeis important. For this reason, the spacing of the weight elements, amongother things the shape, size, and placement, is important. The panelmust sink in so that it represents a flat transition between panel andocean floor, otherwise new scour occurs there. Folds in the panel, evenif they are very small, can lead to undermining of the scour protectionand to damage to the offshore construction to be protected.

The mass of the weight elements can amount to between 50 and 500 kg/m,depending on the application case, according to studies that have beenundertaken. Here, too, the conditions of use are the deciding factor.

A hydrodynamically advantageous shape is understood to mean that thepanel or the panels, also as the result of possible reinforcements, sinkonly in the intended direction, so that with reference to the current,an inclined surface or a slightly curved surface away from the offshoreconstruction, at an incline ratio between 1:4 and 1:5, is formed.Experiments have shown that no scour occurs at this incline.

The ocean floor is not constant in terms of its height. Debris istransported. This means that the ocean floor around the offshoreconstruction can certainly decrease in height by approximately 2 m,depending on the location. If this happens, an incline of 1:5 has beenbrought about over the width of the panel, to be dimensioned in advanceat 2 m, sinking at 1:5=10 m. In this connection, the outside diameter atthe foot of the panel, and thereby the circumference, is decreased. Anynormal elastic material would develop folds in this connection, but thisis not the case for the material selected. This material is able tobalance out the length changes internally within the material. Viceversa, the material is able to stretch: if the ocean floor sinks only onone side of the offshore construction, the apparatus is able to adapt tothe sinking ocean floor and to stretch. Also, the apparatus is able toeven out depressions within the surface to be protected.

The reinforcements can be external reinforcements or reinforcementsintegrated into the panel. These can have a spacing of approximately 2to 3 m on the outside, at the edge of the panel, if they are externalreinforcements. All the reinforcements are disposed to run outward instar shape from an imaginary center point of the foundation to beprotected, whereby the outer contour should have a round or anapproximately round shape, if at all possible, if the ocean floor isknown to sink, in order to prevent fold formation at the edge of thepanel.

In the case of monopiles, the outside diameter of the apparatus isapproximately three times as great as the diameter of the pile.

If the ocean floor sinks, undermining of the panel, at certain points oron the circumference, is intended. However, this will only happen untilthe sand under the panel no longer withstands the weight pressure of thepanel with the weight elements, as the result of liquefaction of thesand, and sinks. In this connection, curvature of the panel, as shown,is also permissible. This can take place at certain points orcompletely. The elasticity of the rubber adapts to the ocean floor andforms a seal on the outside, at the row of weights, once again. Thefoundation is therefore protected once again. If the ocean floor sinksby 2 m, the expanse of the panel from the foundation body into the oceanis 10 m at an incline of 1:5. If this dimension suffices to absorb scoureddies of the foundation under the above conditions, the size of thepanel has thereby been established.

The scour protection panel must be affixed on the body to be protected,in water-tight manner. If this does not happen, and if a gap of only onecentimeter is formed, enormous scour develops through this gap anddamages the stability of the foundation to be protected.

The weight elements at the edge consist essentially of metal. The weightelements have the task of weighing down the edge of the panel in such amanner that the panel sinks into the ocean floor at the ends, withoutcausing any scour there. The greatest possible weight can be implementedwith the metal weights, in relation to the flow cross-section. This alsomeans that the smallest possible flow resistance is present at therequired weight size. Among other things, this is the reason why theweight elements are disposed in such a manner, viewed from the edge inthe direction of the center of the foundation. The longitudinal axis ofthe weight elements always points in the direction of the foundation.

However, the special shape of the weight elements, together with theirdimensions, also has other reasons. The panel or the panels connectedwith one another have the task of adapting to every contour of theground, at least at the edges. Therefore the weight is not allowed tobecome too broad. On the other hand, the apparatus, with the weightelements screwed onto it, must still be so flexible that it adapts toany unevenness of the ground, specifically to both positive and negativechanges or bumps in the ground. Depending on the conditions of oceandepth, current velocity, wave stress, and ground composition, the weightelements have a mass of 50 to 500 kg/m.

The weight elements can be shaped. However, if the panel is smaller indiameter, development of a fold is unavoidable. In order for this not tocause damage, the fold is predetermined in the downward direction. Thisis achieved by means of the special shape of the weight elements with alower indentation. In this connection, the panel is stretched, at first.As it sinks, the panel relaxes. As it sinks further, it will developmany small folds as a result of the predetermined shape, but these aredirected downward and will press themselves into the sand. This effectsuffices to obtain an incline as desired, if the panel has been designedcorrectly. If the distance between the weight elements becomes toogreat, the fold is pushed upward as the result of sand pressure. Thescour protection then becomes non-tight at the edge. If sinking of theocean floor is not expected, the weight elements can be used without anindentation, and reinforcements are also not necessary. However, thesereinforcements can also be used to fold up the scour protection fortransport at sea, and thereby to obtain logistical advantages.

One or more flexible reinforcements can be provided for the apparatus,the rigidity of which is preferably adjustable. A reinforcementcomprises a reinforcement profile composed of flexible plastic, areinforcement wall composed of rubber, disposed above the reinforcementprofile, which wall preferably has a woven fabric insert and forms aclosed cavity that is filled with a medium such as water or air. Therigidity of the flexible reinforcement can be changed or adjusted bymeans of the selection of the thickness of the reinforcement profileand/or the reinforcement wall, as well as by means of the selection ofthe medium and/or its pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

The figures of the drawing show, in detail:

FIG. 1 a top view of the apparatus 1 with a monopile 2;

FIG. 2 partial views of another embodiment of the apparatus 1′ invertical section;

FIG. 3 a weight element 4 in longitudinal section a, in cross-section b,and in a top view c;

FIG. 4 a weight element 4 with an indentation 9 in longitudinal sectiona, in cross-section b, and in a top view c;

FIG. 5 a a vertical section through the apparatus 1 with weight elements4 with an indentation a and with weight elements without an indentation9;

FIG. 5 b a vertical section through the apparatus 1 with weight elements4 without an indentation; and

FIG. 6 a perspective detail view, horizontally cut, of a furtherembodiment of the apparatus 1 with a flexible reinforcement 18.

DETAILED DESCRIPTION OF THE INVENTION

In the following, a best embodiment of the invention will be describedin detail, making reference to the drawings, whereby furtheradvantageous characteristics can be derived from the figures of thedrawing. Functionally equivalent parts are provided with the samereference symbols.

FIG. 1 a shows a top view of the apparatus 1 with a monopile 2. Thisapparatus consists of elastic panels 3 composed of rubber, connectedwith one another, having a thickness of one to two cm. The panels 3 canbe connected with one another by means of vulcanization or by means ofsuitable fastening means (not shown) that have a shape-fit effect. Theelastic panels 3, connected with one another, have the shape of a diskhaving a circular contour and a circular, central opening 11. Theoffshore construction 2 to be protected, namely a monopile of a windpower plant, is disposed in the central opening 11. In this connection,the radius of the apparatus 1 is about three times as long as the radiusof the offshore construction 2, specifically with reference to thehorizontal plane in which the apparatus 1 is fastened onto the monopile2, namely at the level of the ocean floor 8.

The disk formed from the rubber panels 3 is fastened onto the monopile 2in water-tight manner, so that no sea water can penetrate through thecentral opening 11 underneath the apparatus 1. The elastic panel 3 orthe elastic panels 3 composed of rubber lie on the ocean floor 8,whereby uneven areas of the ocean floor 8 can be evened out by means ofthe elasticity.

Weight elements 4 are fastened onto the panels 3 at the edge regionalong the circumference of the apparatus 1, which elements press thepanels 3 downward into the ocean floor at the edges, and thereby sealthem off. In this way, effective scour protection is achieved. Forreasons of a clear illustration, the weight elements 4 are shown only ontwo opposite circle segments, but in fact weight elements 4 are providedalong the entire disk edge 13.

The weight elements 4 have an essentially rectangular base surface. Theweight elements 4 are oriented on the panels 3 in such a manner that the(imaginary) longitudinal axis 12 of each weight element 4 extends in thedirection of the offshore construction 2 and therefore all thelongitudinal axes 12 meet in the center of the apparatus 1 or themonopile 2.

FIG. 1 b shows a detail from FIG. 1 a in a detailed view. Five weightelements 4 are shown, which are disposed at the edge of a circle segmentof the panels 3, whereby the circumference 5 of the circle segmentamounts to about one meter. The weight elements 4 have a width of aboutseventeen centimeters, in each instance, and a distance 6 between themof about three centimeters. The total mass of the weight elements 4amounts to about fifty to five hundred kilograms per meter ofcircumference 5, in other words about ten to one hundred kilograms perweight element 4.

FIG. 2 shows partial views a, b, c, of another embodiment of theapparatus 1 in vertical section. This apparatus has reinforcementelements 7 on the underside. It is shown that the rubber panels 3 shouldbe fastened onto the foundation body of the offshore construction 2 intight manner.

FIG. 2 b shows an ocean floor that has sunk away by about two meters.

In FIG. 2 c, it is shown how the elastic panels 3 are pressed downwardby the weight elements 4, so that sealing takes place and the offshoreconstruction 2 is protected against scouring. If the ocean floor sinksby two meters, the length of the panel from the foundation body 2 outamounts to about ten meters at an optimal incline of about 1:5.

In FIG. 2 d, an apparatus 1 without reinforcement elements 7 is shown.This results in a curved shape 14 of the panels, which is fundamentallyhydrodynamically advantageous. However, in the case shown, the curvature14 is overly marked, so that scour-promoting eddies are formed. A lessercurvature 14′ as shown with a broken line in FIG. 2 c is moreadvantageous. This can be adjusted by means of the selection of the massof the weight elements 4.

FIG. 3 a shows a weight element 4 in longitudinal section, FIG. 3 b incross-section, and FIG. 3 c in a top view. The weight element 4 has thebasic shape of a block that narrows upward, which has the shape of anequilateral, symmetrical trapezoid in longitudinal section and incross-section. The weight elements 4 shown have a length of 3.80 m and awidth of the of 1.70 m, with reference to their base surface. The blocknarrows quantitatively in such a manner that a deviation from thevertical of about 15 degrees occurs. The corners are furthermore roundedoff. This results in an advantageous hydrodynamic shape, on the onehand, because no eddies and disadvantageous currents of the ocean wateroccur at the weight elements 4. A further, significant advantage of theshape that narrows upward consists in that sections of the panels 3 canelastically sink downward without the weight elements 4 then coming intocontact in the region of a curvature.

The weight elements 4 furthermore have two continuous openings 15 forthe introduction of fastening elements (not shown). In this way, theweights can be permanently fastened onto the rubber panels 3. Even ifthe rubber panels 3 sink down and if a slant or curvature forms, asshown in FIGS. 2 c and 2 d, secure fixation is guaranteed.

Furthermore, two lower recesses 17 are provided for a weight element 4,in each instance. These serve as an assembly aid and facilitate grippingof the weight element 4 when it is supposed to be transported andafterward fastened onto the elastic panels 3.

FIG. 4 a shows another embodiment of the weight element 4 inlongitudinal section, FIG. 4 b in cross-section, and FIG. 4 c in a topview. In the case of this embodiment, the weight element 4 has anindentation 9 that is curved inward or upward, in concave manner, on itsunderside.

FIG. 5 a shows a vertical section through an apparatus 1 having weightelements 4 having a lower indentation 9. The weight elements 4 thereforecorrespond to the embodiment shown in FIGS. 4 a, 4 b, and 4 c. Theweight elements 4, which are shown in cross-section, are fastened ontothe top of the elastic panels 3 and permanently fixed in place.

Experiments have shown that in the case of the weight elements 4 shownin FIG. 5 b, without a lower indentation 9, folds that face upward, inother words elevations in the elastic panels 3 (not shown) can be formedunder certain conditions, if the panels 3 sink down, as the result ofthe sand pressure between the weight elements 4. The scour protectionthen becomes non-tight at the outer edge 13 of the apparatus 1, as aresult of the folds or elevations.

It is true that fold formation 10 between the weight elements 4 occursalso as the result of the indentations 9 shown. However, the folds 10 inthe elastic panels 3 between the weight elements 4 point downward, inother words they are bent in the direction toward the ocean floor in theregion of the interstices 16, so that depressions 10 are formed as aresult. This occurs in that the indentations 9 form a concave guide forthe rubber panels 3, thereby shaping the rubber panels 3 in wave-likemanner, as shown in FIG. 5 a. In this way, harmful fold formation upwardis avoided in the region of the interstices 16, and the apparatus 1forms a seal also in the edge regions, and protects offshoreconstructions 2 against scouring.

FIG. 5 b shows weight elements 4 without indentation. If greater sinkingof the ocean floor and thereby fold formation downward is not expected,this embodiment of the weight elements 4 can be used.

FIG. 6 shows a perspective detail view, horizontally cut, of a furtherembodiment of the apparatus 1 having a flexible reinforcement 18. Thelatter comprises a reinforcement profile 19 composed of flexibleplastic. The reinforcement profile 19 is fastened onto the elasticpanels 3 using suitable fastening means. A reinforcement wall 20composed of rubber is disposed above the reinforcement profile 19, whichwall can have a woven fabric insert and is tightly fastened onto thepanels 3. Fastening can take place, in each instance, by means ofadhesives or vulcanization.

The upper reinforcement wall 20, together with the elastic panels 3,forms a closed cavity 21 that is filled with a medium. Water or air, forexample, is a possible medium. The rigidity of the flexiblereinforcement 18 can be changed or adjusted by means of the selection ofthe thickness of the reinforcement profile 19 and/or reinforcement wall20, as well as by the selection of the medium and/or its pressure.

REFERENCE SYMBOL LIST

-   1. apparatus-   2. offshore construction-   3. elastic panels-   4. weight elements-   5. circumference-   6. distance between the weight elements-   7. reinforcements-   8. ocean floor-   9. indentation-   10. fold-   11. central opening-   12. longitudinal axis-   13. edge region-   14. curvature-   15. fastening openings-   16. interstice-   17. recess-   18. reinforcement-   19. reinforcement profile-   20. reinforcement wall-   21. cavity with medium

1. Apparatus (1) for scour protection of offshore constructions (2),which comprises one or more elastic panels (3) composed of rubber andweight elements (4) that are fastened onto the panels (3) by means offastening means.
 2. Apparatus (1) according to claim 1, wherein theelastic panel (3) or the elastic panels (3) composed of rubber have athickness of one to two centimeters and/or the weight elements (4) arefastened onto the elastic panel (3) or the elastic panels (3) at theedge region of the apparatus (1).
 3. Apparatus (1) according to claim 1,wherein the elastic panel (3) or the elastic panels (3) connected withone another form a disk with a circular or approximately circularcontour, at the center point of which the offshore construction (2) isdisposed.
 4. Apparatus (1) according to claim 1, wherein the radius ofthe apparatus (1) is about three times as long as the radius of theoffshore construction (2) in the plane in which the apparatus (1) isdisposed.
 5. Apparatus (1) according to claim 1, wherein the weightelements (4) have an essentially rectangular base surface, thelongitudinal axis of which points in the direction of the offshoreconstruction (2), in each instance.
 6. Apparatus (1) according to claim1, wherein the weight elements (4) consist essentially of metal. 7.Apparatus (1) according to claim 1, wherein the weight elements (4) havethe shape, in longitudinal section and/or in transverse section, of anequilateral, symmetrical trapezoid, wherein its corners are preferablyrounded off.
 8. Apparatus (1) according to, wherein the weight elements(4) have an indentation (9) on the underside, which is domed inward, inconcave manner, in cross-section.
 9. Apparatus (1) according to claim 1,wherein at least one flexible reinforcement (17) is provided, whichcomprises a reinforcement profile (19) and a reinforcement wall (20)disposed above the reinforcement profile (19), wherein the reinforcementwall (20) forms a closed cavity (21) that is filled with a medium.